A number of IgE-reactive proteins have been identified in natural and processed latex products. Hev b 5 an acidic protein in the cytoplasm of lacticifer cells of rubber trees, is demonstrated to be a potent allergen in eliciting allergenic reactions in humans. This acidic protein, Hev b 5, was found in extracts prepared from brands of gloves. When purified the protein elicits histamine release from passively sensitized human basophils. The cDNA coding for this protein was isolated and sequenced from a latex cDNA library. The deduced amino acid sequence shows a high degree of homology to an acidic protein in kiwi fruit. The sequence homology between these two acidic proteins provided a molecular explanation for the high frequence of fruit hypersensitivity in latex allergenic patients.